It's a 2000 civic lx with 265k miles. Changed the gas cap as diagnosted by auto zone because engine light came on. Then I decided to tune it up and changed the air filter plugs cap and rotor. Car runs better but it won't hold a idle when I come to a stop. I did disconnect the battery when I changed the cap and rotor and to eliminate the check engine light, which it did. Please advise

 

What was/were the DTC code(s) thrown when the Check Engine Light came on?

 

What do you mean by not holding idle? Does it stall? Does it hunt for correct idle and not stall? Do rpms surge up and down at idle?

If it's stalling; Can you hear the fuel pump priming? If, so loosen banjo bolt on the fuel filter and have helper turn key to position 2 ..watch for fuel to come out of lossened banjo bolt. Should come oout at a good, steady rate. Better yet would be to use a live data scanner and get fuel psi (38-42 psi). If you don't have a live data scanner either by one or call and independant shop that does have one that'll work for your specific car. Stalling can be caused by several possibilities: running lean, cylinder misfires, improper fuel delivery, weak spark, mechanical timing.

 

This here. OP you need to get your car putting around the neighborhood. Let it intentionally stall when it tries to. Restart the car, drive a block or two, see if you can get it to stall again. Then check engine codes. Even if your check engine light isn't on the computer could have some new codes stored in it. This will work wonders at getting you pointed in the right direction. A million things can cause a car to stall. Also, does the idle surge up and down, or is it REALLY LOW, or is it just normal and just coughs out and dies? The more details you provide the better, don't be afraid to use your keyboard.

 

ALSO, IS YOUR CAR A MANUAL TRANSMISSION OR AUTOMATIC?????